Centrifugal pump and a static seal thereof

ABSTRACT

The present invention relates to a centrifugal pump and a static seal of the dynamic sealing thereof. The invention especially relates to modifying the attachment of said static seal and a seal cover acting as a counter ring thereof in such a way that, for example, when the static seal wears, the clearance thereof can be adjusted without a need to stop the pump. A characteristic feature of a centrifugal pump in accordance with the invention, comprising, among other things, a pump housing ( 72 ), a shaft ( 12 ), an impeller arranged on the shaft and a dynamic seal ( 30, 32 ) arranged in connection with the shaft ( 12 ), and a static seal arranged in connection with the shaft ( 12 ) behind the dynamic seal as seen from the impeller, said static seal comprising a flexible seal means ( 50 ) on the shaft ( 12 ) and a stationary counter ring thereof, is that a seal cover ( 62 ) including a stationary counter ring ( 60 ) is adjustable in the axial direction of the pump.

The present invention relates to a centrifugal pump and a static seal ofdynamic sealing thereof. The invention especially relates to modifyingthe attachment of said static seal and a seal cover acting as a counterring thereof in such a way that, for example, when the static sealwears, the clearance thereof can be adjusted without a need to stop thepump.

A dynamic sealing is a sealing arrangement, which is able to without anymechanical contact seal a centrifugal pump during its operation so thatno liquid leaks along the shaft towards the bearings and the drive.Other sealing arrangements for the same purpose are, for example,braided packings and slide ring seals, which both require mechanicalcontact between the rotary and stationary surface. In other words, it isclear that the above-mentioned seal types based on continuous mechanicalcontact suffer at some point of their life cycle from wearing problems.

A dynamic sealing is located behind the pump volute in front of the pumpbearing (seen from the suction duct) in an annular chamber arranged inconnection with the rear wall of the pump. Said chamber is in directflow connection with the pump volute, where the pump impeller rotates. Arotary disc attached on the pump shaft divides said chamber to animpeller side cavity and a pump bearing side cavity. Said disc isprovided with vanes facing the bearing side cavity, whereby it can alsobe called a repeller, whereas the other side of the disc is even.Considering a case where said annular chamber contains liquid, the vaneson said disc tend to pump the liquid first radially outwards and thenaround the outer edge of the disc to the impeller side cavity of thechamber. However, now that the pump is in operation, the pressuregenerated in the pump volute by the impeller effects to the oppositedirection, i.e. the impeller forces liquid towards the bearings.Thereby, an equilibrium can be found where a liquid ring rotated by theabove mentioned repeller vanes compensates the pressure generated by theimpeller and the pump is sealed in such a away that no liquid enters theshaft space of the chamber on the bearing side. However, when the pumpis not running, the liquid to be pumped is allowed to flow freely aroundthe edge of the repeller disc in the chamber to the shaft space andtherethrough to the atmosphere, unless it is prevented in a suitablemanner. This is carried out by a so-called static seal, of which thereare a number of known types. Among others, WO-A1-03/040598 andCA-C-1,3173,29 relate to static seals. The following description,however, discusses two other basic types of a static seal, which can beconsidered the basis of the present invention. In one type, for example,the one illustrated in FIG. 1, a disc, which is manufactured of aflexible material and extends radially towards the pump shaft, isattached to the pump housing or to the cover thereof and has a ringattached on the shaft to act as counter member for the flexible disc.Said ring has been mounted on the shaft in such a way that when theliquid flows from the pump to the shaft space, it presses the flexibledisc against the ring on the shaft, or more precisely against thesealing surface of said ring. Another alternative, which is discussedbelow more in detail, is naturally to arrange a disc of flexiblematerial on the shaft and its stationary counterpart to the pump housingor to the cover of the housing. The operating principle, however,remains the same in both cases.

A disadvantage with the static seal of a dynamic sealing described morein detail above having a flexible disc attached to the pump housing orto the cover of the housing is that when the pump stops, the centrifugalforce pushes the liquid between the counter ring and the static seal.This possibly causes a leakage of the liquid to be pumped and wearing ofthe seals. One solution to the above mentioned problem has beendisclosed in patent specification U.S. Pat. No. 4,973,063, in which twoseal rings, one flexible, the other inflexible, are located on the shaftto prevent the outflow of the liquid in connection with the dynamicsealing, while the pump is running. Both seals are rotary, and thepurpose of the inflexible seal ring closer to the dynamic sealing is toprevent the liquid from flowing to the outer seal ring acting as themain seal, and therethrough, further out. Since both seals have beenassembled on the shaft inside the pump housing the possible adjustmentof the clearance is difficult and can be performed only by stopping thepump.

A static seal of the dynamic sealing typically used as the shaft seal ofa centrifugal pump is, as described above, formed of a stationarilyassembled, flexible disc, and a rotary counter ring attached with alocking screw to the shaft. Below, there is a list of a number ofdisadvantages of such a construction affecting the operation of thepump:

-   -   When the pump stops running, the centrifugal force expedites the        escape of the liquid and the particles entrained therewith        between the rotary counter ring and the static seal causing        leakage of the liquid to be pumped and wearing of the seal.    -   When the static seal wears, the pump must be stopped, because        the counter ring of the static seal is attached on the shaft.        The locking screws typically used for the attachment of the        counter ring must be loosened and thereafter the counter ring        must be moved to a new position for the static seal. This kind        of adjustment is a very time-consuming and cumbersome task.    -   In a prior art solution, means for the collection of leakage        splashes and a shaft cover are missing. If the structure were        provided with a cover against splashes and contact with the        shaft, it should be removed always before the adjustment of the        counter ring clearance. The arrangement would be complicated,        expensive and difficult to use.

According to the invention, by turning the above disclosed constructionthe other way round in such a way that the flexible plate which acted asa static seal member in the prior art arrangement is made rotary, isdesigned to be applicable for the purpose, and by locating it in theshaft space and by manufacturing the counter ring, which rotated in theprior art arrangement, as a static seal member and by locating it in theaxial direction further away from the impeller, for example, followingadvantages are achieved:

-   -   When the pump is stopped, but is still rotating, the centrifugal        force is made to transfer liquid to be pumped together with the        particles possibly entrained therein away from the proximity of        the sealing point of the static seal, whereby leakages of the        liquid and wearing of the seals are reduced.    -   When the static seal wears, it is possible to adjust the        clearance thereof while the pump is running, because it is        possible to arrange the adjustment in connection with a seal        cover attached to the cover of the pump housing or to the        housing, which seal cover operates as a counter member of the        static seal. Thereby, the adjustment can be performed more        quickly than in the conventional arrangement.    -   According to a preferred embodiment of the invention, the shaft        is protected from the liquid to be pumped and if the seal leaks,        it is possible to collect the splashes to the seal cover and        lead such in a controlled manner therefrom to a leakage        collection system. The seal cover may also be designed such that        the rotary shaft can be covered, whereby the shaft will neither        be a risk in the adjustment of the seal clearance nor will it        prevent from performing the adjustment, as was the case in the        prior art solutions.

The present invention aims at eliminating at least some of the problemsand disadvantages of the prior art centrifugal pumps by disclosing, forexample, a static seal to be applied in a centrifugal pump. By usingsaid static seal, it is possible, when the pump is stopped, but is stillrotating, to make the centrifugal force to transfer liquid to be pumpedtogether with the particles possibly entrained therewith away from theproximity of the sealing point of the static seal, whereby leakages ofthe liquid and wearing of the seals are reduced. It is a typical featureof a centrifugal pump in accordance with the invention and a static sealused in connection therewith that when the static seal wears, theclearance thereof may be adjusted, while the pump is still running.

Other characteristic features of a centrifugal pump and a static sealthereof in accordance with the present invention will become clear inthe accompanying claims.

The centrifugal pump in accordance with the present invention and thestatic seal thereof are discussed more in detail below, by way ofexample, with reference to the accompanying drawings, in which

FIG. 1 schematically illustrates a static seal in accordance with theprior art, in connection with a centrifugal pump; and FIG. 2schematically illustrates a static seal in accordance with the presentinvention in connection with a centrifugal pump.

FIG. 1 schematically illustrates a conventional construction for astatic seal of a dynamic sealing of a centrifugal pump in accordancewith the prior art. An impeller (not shown in the drawing) of acentrifugal pump pumps liquid entering the pump from the left along asuction duct to a pressure opening of the pump volute. The impeller isattached to a pump shaft 12, which is mounted with bearings to theright, the part being already cut away, to the pump housing. The spacein the pump behind the impeller is limited by a pump rear wall 20. Adisc 30 attached to the pump shaft 12, located in an annular sealingchamber 32 arranged in connection with the rear wall 20 of the pump actsas dynamic sealing of the pump, and is called a repeller. The rotarydisc 30 i.e. the repeller attached to the shaft 12 divides the chamber32 to an impeller side cavity 34 and a pump bearing side cavity 36 insuch a way that there is a flow connection between said cavities outsidethe outer edge of the rim of the disc 30. Said disc 30 is provided withvanes 38 on the side facing said bearing side cavity 36 substantiallythroughout the whole radial dimension of the disc, while the oppositeside is even. The purpose of the repeller vanes 38 is to pump liquid inthe bearing side cavity 36 outwards towards the impeller side cavity 34,which again is affected by the pressure generated by the impeller of thepump reduced by the counter pressure generated by the rear vanes of theimpeller. In other words, the vanes 38 of the repeller generate apressure affecting from cavity 36 to space 34 and towards the impellerof the pump, by means of which the pressure prevailing in the spacebehind the impeller is balanced.

A typically used static seal of the above described dynamic sealing of acentrifugal pump is a flexible static plate or disc 40 arranged behindthe dynamic sealing as seen from the impeller, which static plate ordisc is attached by means of a ring 46 and bolts or headless screws 48to the pump housing or the cover of the housing, and which, when thepump stops, is pressed against a counter ring 42 of the rotary staticseal 40 on the shaft 12 and prevents liquid from flowing out of thepump. In other words, the liquid entering from the direction of theimpeller (from the left in the drawing), thus, presses the seal disc 40against the counter ring 42. The counter ring 42 is attached on theshaft 12 with one or more screws. Problematic situations, such as thoselisted in the introductory part of the description occur, for example,when the pump is stopped, but is still running whereby the centrifugalforce pushes the liquid entering a shaft space 44 on the side of thebearing after the dynamic sealing, between the static seal disc 40 andthe rotary counter ring 42. The described seal is of such a constructionthat solid material that has entered the range of the surface of therotary counter ring 42 tends to flow outwards along the surface due tothe centrifugal force, whereby it enters the clearance between therotary ring and the seal disc. While being therebetween, the solidmaterial either erodes the surfaces, mostly the seal disc, or when themutual movement between the surfaces stops, it leaves a gap between thesurfaces, wherefrom liquid in the seal space is allowed to leak out.

FIG. 2 illustrates a seal arrangement in accordance with a preferredembodiment of the invention. According to the invention, the structureof the known static seal arrangement of FIG. 1 is changed opposite insuch a way that the flexible plate 40 that acted as a static seal memberis redesigned and made rotary and the rotary stationary counter ring 42is now manufactured as a static seal member. A novel, flexible sealmeans 50 is located on the pump shaft behind the dynamic sealing and it,among other things, prevents, according to a preferred embodiment of theinvention, the shaft 12 from coming into contact with the liquid to bepumped. A novel, static, i.e. stationary counter ring 60 in accordancewith the invention is naturally located behind the flexible seal means50 as seen from the impeller of the pump. As the flexible seal means 50of the new static seal is rotary, it is possible, by means ofcentrifugal force, to keep liquid and particles possibly entrainedtherewith away from between the rotary seal means and the static sealmeans.

The flexible seal means 50 of the static seal is of its form, accordingto a preferred embodiment of the invention, a tubular cylinder having aneven diameter at the part 52 facing the pump impeller, followed by aconstricted part 54 which has a smaller diameter than the part 52, thepurpose of which part 54 is to ensure the flexibility of the seal, andfurther followed by a lip 56 having a larger diameter and facing thestationary counter ring 60. The axial dimension of said seal lip 56 isless than that of the part 52. Further, the axial dimension of the lip56 diminishes towards the radially outer tip of the lip. A sealingsurface 58 of the flexible seal means 50, which is preferablysubstantially perpendicular to the shaft 12 and which is pressed againstthe end surface of the counter ring 60, may be either straight or atleast partially inclined while the tip of the lip 56 is closer to thesurface of the counter ring. When the sealing surface 58 is inclined bya suitable dimensioning, the tip of the lip tends to turn outwards, dueto the centrifugal force, when the pump is started, and, at the sametime, slightly away from the counter ring 60, in other words spacedapart from the counter ring 60, whereby wearing of the static seal canbe reduced.

The counter ring 60 which is a part of an annular seal cover 62 attachedto the cover of the pump housing or to the housing 72 acts as acounterpart of the flexible seal means 50 of the static seal. The sealcover 62 is attached to the pump housing or to the cover of the housingby means of a flange 64 extending from an otherwise substantiallytubular seal cover 62. The flange 64 is provided with openings requiredfor attachment bolts or headless screws 66, by means of which the sealcover is attached to the pump housing 72 or the cover of the housing.There can be one or more, preferably however three, attachment points,for the seal cover 62 acting as a second part of this static seal.Thereby, it is possible to adjust the static seal by means of theheadless screws 66 and the nuts 68 driven to them. The adjustment hasbeen arranged in connection with the seal cover 62 attached to the coverof the pump housing or to the housing, whereby, when the static sealwears, the clearance thereof can be adjusted while the pump is running.Thereby, the adjustment can be performed more easily and quickly thanwith the conventional solution.

According to FIG. 2, the flexible seal means 50 of a static sealprotects the shaft 12 from the liquid to be pumped. If the flexible sealmeans 50 is humidity-permeable or leaks towards the bearing, it ispossible, according to a preferred embodiment of the invention, tocollect the leakage to a seal cover 62 operating as a counterpart of theflexible seal means 50 and, further, remove therefrom in a controlledmanner to a collection system 70. The seal cover 62 can be extendedtowards the pump bearing, as is tentatively disclosed in the drawing, sothat the rotary shaft 12 may be covered with the seal cover, wherebythere is no risk of touching the rotating shaft when adjusting theclearance of the static seal, nor does it prevent the adjustment of theclearance, as was the case in the prior art solutions.

It must be noted from the above description that the seal cover with itscounter ring and flange and extension is illustrated as one unitarymember. It is, of course, possible that the seal cover is made ofseveral elements. It is, for example, possible that the counter ring isa separate part attached together with the flange and shaft cover whenassembling the seal. In the similar way, also other modifications arepossible. It is, for example, possible that the shaft cover is not anintegrated part of the seal cover, but a separate part utilizing theattachment bolts and headless screws thereof in the attachment.

As can be seen from the above description, it has been possible todevelop a static seal which is more versatile than the previous staticseal arrangements, said arrangement enabling, for example, theadjustment of the seal clearance while the pump is running. While theinvention has been herein described by way of examples in connectionwith what are at present considered to be the preferred embodiments, itis to be understood that the invention is not limited to the disclosedembodiments, but is intended to cover various combinations and/ormodifications of its features and other applications within the scope ofthe invention as defined in the appended claims.

1. A centrifugal pump, comprising a pump housing (72), a shaft (12), animpeller attached on the shaft, and a dynamic sealing (30, 32) arrangedin connection with the shaft (12), and a static seal arranged inconnection with the shaft (12) behind the dynamic sealing as seen fromthe impeller, said static seal comprising a flexible seal means (50) onthe shaft (12) and a stationary counter ring thereof, characterized inthat a seal cover (62) including a stationary counter ring (60) isadjustable in the axial direction of the pump.
 2. Centrifugal pump inaccordance with claim 1, characterized in that the clearance of thestatic seal may be adjusted while the pump is running.
 3. Centrifugalpump in accordance with claim 1, characterized in that a seal cover (62)is attached to a pump housing (72) and/or to a cover of the housing bymeans of adjusting means (64, 66, 68).
 4. Centrifugal pump in accordancewith claim 1, characterized in that said adjusting means comprise aflange (64) of the seal cover and the attachment bolts or headlessscrews (66) with nuts (68).
 5. Centrifugal pump in accordance with claim1, characterized in that an extension of the seal cover (62) towards thepump bearing acts as shaft cover.
 6. Centrifugal pump in accordance withclaim 1, characterized in means for collecting liquid leaking from thestatic seal to the seal cover (62) and for leading such further to aleakage collection system (70).
 7. Centrifugal pump in accordance withclaim 1, characterized in that the flexible seal means (50) of thestatic seal is located on the pump shaft, and is formed of a cylindricalportion (52), an annular constricted portion (54), and a lip (56). 8.Centrifugal pump in accordance with claim 1, characterized in that saidseal means (50) prevents the liquid to be pumped from getting intocontact with the pump shaft (12).
 9. A static seal to be used inconnection with a dynamic sealing of a centrifugal pump, said staticseal comprising a flexible seal means (50) and a stationary counter ringthereof, characterized in that the counter ring (60) is a part of theseal cover (62) together with a flange (64), by means of which flangethe clearance of the static seal is adjusted.
 10. Static seal inaccordance with claim 9, characterized in that the flexible seal means(50) of a static seal to be assembled on the shaft is formed at its oneend of a substantially cylindrical portion (52), of an annularconstricted portion (54) and, at its other end, of a radially outwardsextending lip (56) of the seal means (50), one side of which forms anend surface (58) of the seal means (50) and operates together with thecounter ring (60).
 11. Static seal in accordance with claim 10,characterized in that said end surface (58) is substantially radial. 12.Static seal in accordance with claim 9, characterized in that the endsurface (58) of the seal means (50) is inclined either completely orpartially.
 13. Static seal in accordance with claim 8, characterized inthat said radially outermost part of the lip (56) forms the tip of thelip, which is in contact with the counter ring (60) when the seal is inoperation.
 14. Static seal in accordance with claim 9, characterized inthat said tip of the lip (56) extends axially further than the rest ofthe lip.
 15. Static seal in accordance with claim 9, characterized inthat the seal cover (62) is substantially cylindrical of its form,forming a shaft cover.
 16. Static seal in accordance with claim 9,characterized in that the seal cover is provided with means for guidingthe leakage liquid to a leakage collection system.